Design And Performance Research Of Close-Chain Multi-Legged Mobile System

With the development of technology and the spreading range of human activities,the demands for the mobile systems are increasing,and different mobile systems are playing a more and more important role.Currently,unmanned ground mobile systems are widely used in the application scenarios such as resource detecting,logistics,disaster rescuing and military actions.To overcome the different terrains in the environments,people have high demands for the reliability,ground adaptivity and the endurance.Compared to the wheeled and tracked mobile systems,the legged mobile systems have the unique performances for the feet touch the ground in isolated points,which is special.Based on the linkages with a single degree of freedom,the dissertation designs the mobile systems in different levels.Fully taking the advantage of the simple control system,the low degree of freedom,the high integral stiffness and low power consumption,the mobile system is designed and optimized to gain the capabilities such as high-speed walking,large size obstacle climbing and smoothly walking.The detailed research contents are listed as follows:(1)The design method of the close-chain multi-legged mobile system is proposed.Firstly,based on the creative design of mechanical devices,the type synthesis of(6,7)and(8,10)kinematic chains are analyzed and the atlas of specialized mechanical leg design is obtained.Secondly,the design method in the unit level and the complete mobile system level is put forward.By listing all combinations of the mechanical legs,the multi-legged walking units are formed,and then,the complete mobile systems are formed with the combination of the multi-legged walking units.Each combination is coded according to the configurations and the combination features.After that,mathematical modeling of the kinematic chain and the trajectory optimization are conducted,and the performance are tested in the applications.Finally,the overall design target and the evaluation of the mobile system are given as the instructive reference for the detailed design.(2)Research on the performance of walking smoothness of the close-chain multilegged mobile system is carried out.Firstly,the fluctuation model is established based on the kinematic analysis and the undesired movements are calculated.The compensation movement is obtained inversely.Cam-follower mechanism is used to compensate for the flexible design.Secondly,the fluctuation along vertical and the horizontal directions are separated analyzed.Thirdly,the input of the compensation cam mechanisms share the same motion input with the crank link and realized the compensation without introducing extra degree of freedom.Lastly,the mobile system prototype is fabricated and the performances are tested.(3)Research on the high-speed moving performance of the close-chain multi-legged mobile system is carried out.First,the kinematic analysis is done and the max effective walking speed is calculated with the commonly used fix-point design.One of the bottle necks to increase the walking speed is the displacement fluctuation along vertical direction.Secondly,taking advantage of the monotonicity of the pitch angle of the foot link during the supporting phase,curved foot-ground contact interface is proposed.The shape of the curve is formed with the envelope the virtual ground in the foot link coordinate system.Thirdly,the effect of the different configuration of the mechanical legs is detailed discussed.Lastly,the prototype is fabricated.The results show that the prototype walks at the high speed with low vertical fluctuation.(4)Research on the obstacle climbing performance of the close-chain multi-legged mobile system is carried out.For the mechanical leg with a single degree of freedom,the foot end trajectory and the step height are fixed,which limits the trafficability facing the large sized obstacle.To increase the trafficability and environment adaptivity in large scale,attitude adjustments are introduced.To gain the promotion of the step height with small amount of the actuators,different feasible configurations are revealed and discussed.The obstacle climbing strategies for different configurations are analyzed,and related obstacle climbing parameters are compared and the optimal scheme is decided.For the uncertainty of the initial position in the obstacle climbing process,the probability model is established,and the adjustment parameters are given according to the different obstacle sizes.Finally,the mobile system prototypes are built.The obstacle climbing experiments show that the pitch adjustive leg unit increase the trafficability.